The present invention relates to a photosensitive resin composition suitable for use as a solder resist composition applicable to the manufacture of rigid and flexible printed circuit boards or LSI packages such as BGA (ball grid array), CSP (chip size package), etc.
Solder resist is used in the manufacture of printed circuit boards, and in the recent years it is used also in the field of new LSI packages such as BGA, CSP, etc. A solder resist is indispensably necessary as a protective film for protecting the solder-evading portions from adhesion of solder, or as a permanent mask. Sometimes, soldering is practiced by printing a thermosetting solder according to the screen printing process, and the present invention is applicable to such a method, too. In the recent years, however, photo solder resist method or the method of forming pattern by photography has become more prevalent, because the screen printing method is limited in resolving power and cannot cope with the trend of enhancing the density of wiring. Of the photo solder resists, alkali-development type photo solder resist which can be developed with a solution of weak alkali such as sodium carbonate and the like is predominantly used from the viewpoint of securing the working environment and earth environment. As such alkali-development type photo solder resist, those disclosed in JP-A 61-243869 and JP-A 1-141904 can be referred to. The alkali-development type photo solder resist, however, is yet unsatisfactory in durability. That is, it is inferior to prior thermosetting type or solvent development type of solder resists in chemical resistance, water resistance and heat resistance. This is for a reason that the main ingredient of an alkali-development type photo solder resist composition must be a compound having hydrophilic groups facilitating the permeation of chemical solutions, water and water vapor necessary for alkali-development, due to which adhesiveness between resist film and copper is low. Especially in semiconductor packages such as BGA, CSP, etc., a high resistance to PCT (pressure-cooker test property which may be considered as a wet heat resistance) is needed. The existing alkali-development type photo solder resist, however, can endure such a test of severe condition only for about several hours to ten-odd hours.